Metal tools and implements – making – Blank or process – Cutlery
Reexamination Certificate
2000-07-25
2002-07-23
Watts, Douglas D. (Department: 3724)
Metal tools and implements, making
Blank or process
Cutlery
C030S277400, C030S350000
Reexamination Certificate
active
06422110
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a cutting knife for severing tough, elastic materials, in particular for severing cement beads, e.g. of window panes cemented in motor vehicles or filled in wall joints. The knife comprises a securement portion having a receptacle for securing the cutting knife to an oscillatory drive of a cutting tool, and a cutting portion with at least one cutting edge. The invention further relates to a method for producing such a cutting knife.
DESCRIPTION OF RELATED PRIOR ART
A knife of this type is known from EP-B 0 141 035, while similar knives are disclosed in DE-A 3 626 762 and DE-B 3 838 044. It is well known that such cutting knives are used to remove windshields from motor vehicles when this is necessary due to window damage or leakage of the cement bead. A further application is the removal of leaky silicon joints in brickwork.
Common to the known knives is that when cutting through the cement bead, for example when removing a damaged windshield from a motor vehicle, there is considerable danger of breaking the knife. One reason for this is the tough material of the cement bead which is often made of a certain type of polyurethane. Another reason is the considerable force required especially for cutting through thicker beads, despite the high frequency and the small rotary angle of the oscillatory drive. Wider cement beads occur often for windshields that have already been replaced before, where the cement bead has been applied manually during assembly.
On the other hand, such knives or blades become rapidly dull and must be frequently sharpened due to the very resistant and tough material of the cement bead.
The known knives to date are made of a common steel used for knives. Initially, a flat blank is stamped out of a suitable sheet and is optionally bent when the knife is to have a U-shaped cross section or angled or bent form. Optionally a subsequent treatment by grinding follows. Thereafter, the knife is hardened and ground and optionally polished.
The knife disclosed in EP-B 0 141 035 includes a securement opening in the form of a 12-edged hole for form-fit securement to the drive shaft of an oscillatory drive. In contrast, the cutting knife disclosed in DE-A 3 626 762 is welded to the drive shaft. The knives disclosed in DE-B 3 838 044 are fixed to the drive unit as in the manner of a sabre saw and are driven to oscillate in the axial direction. However, such knives are also made from knife steel, hardened and sharpened before use.
In addition, cutting knives are known through prior use whose surface is provided with a thin layer of titanium nitride, which apparently has been applied by chemical vapor deposition. However, such knives have not proven themselves in practice, since the titanium nitride layer is so thin so as to be practically useless. Already after a single re-sharpening, practically no effect remained. In addition, the production using CVD (chemical vapor deposition) is relatively complicated and expensive. Further, the titanium nitride coated knives are also subject to the above-mentioned problems of breakage.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved cutting knife and a method for producing same, which allows improved cutting capacity and reduced susceptibility to breakage thereby allowing increased utility in operation.
This and other objects of the invention are solved by providing a cutting knife comprising a plurality of flat interconnected layers, where at least two of the layers are of a metallic material. In this manner, the object is achieved in that the multi-layer construction of the knife out of a plurality of individual, flat interconnected metal layers provide improved properties of the knife on the whole. Namely, a particularly high hardness and wear resistance is achieved at the cutting edge or edges and at the same time greatly improved elasticity and reduced breakage is achieved.
It has been known for centuries to produce the so-called Damascus blades, i.e. to produce sabres and daggers from individual layers and to forge these together. Even so, it is not obvious to transfer this method to the production of cutting knives for use in conjunction with an oscillatory drive to cut tough, elastic material.
The cutting knives of the present invention are mass-produced articles which are required in large number in repairing joints in brickwork, in automotive workshops and in glass workshops, since the knives become dull in relatively short time or break. Frequently, a knife can be used only once for cutting out a single windshield.
In contrast, the Damascus blades are handmade and are extremely complicated and expensive in production. Such blades today which consist of numerous individual layers forged together cost three or four digit sums in EUROS. The known knives for use together with oscillatory drives have been used since 1983, however one has not considered the use of a knife with a plurality of metal layers.
It is therefore not obvious to transfer such an expensive and complicated procedure to the production of cutting knives of the present type.
In a preferred embodiment of the present invention, the metal layers are connected to one another by heat bonding, preferably forged to one another.
Although forged metal layers basically have particularly good properties, it is also possible to bond the metal layers in other ways. For example, it is contemplated to surface weld the metal layers, which is possible with a special resistance welding process with simultaneous application of pressure. Friction welding is also possible. More recently, it is also possible to bond the different metal layers for this purpose with adhesives.
In a further embodiment of the present invention, some of the individual layers are made of materials having different properties.
In this manner, the properties of the knife can be “custom-made” in a certain sense. For example, central layers can be provided having a reduced hardness, with high tenacity and bending strength. To the outside, the layers can have an increasing hardness and a decreasing tenacity or bending strength and vice versa. Basically it is possible to provide the different layers out of the same material, but having been treated differently, for example having a different degree of deformation (e.g. using cold rolled or annealed steel). The properties can also be produced when later heat treating the bonded layers. However, it is particularly preferred to use special materials whose composition is adapted to the desired properties. This is to achieve a particularly high elasticity and bending strength in a defined region of the cutting portion and in particular to achieve a high hardness and optionally reduced friction in the outer layers at the cutting edge. In some cases it can also be appropriate to produce the outer layers from a soft and/or particularly elastic material. This is advantageous when the cement bead to be removed is located on a painted surface of plastic or wood.
The outer metal layers can also be subjected to a special surface treatment, for example a treatment with boron, carbon, nitro carbon or the like, to achieve a particular high hardness in the outer layers in the area of the at least one cutting edge.
It is also preferred that at least one of the layers comprises a wear resistant material, preferably wolfram carbide, silicon carbide, titanium carbide, chromium oxide, silicon oxide, titanium oxide, aluminum oxide, boron nitride, titanium nitride, molybdenum or mixtures thereof or mixtures and alloys with further metals.
The additional wear resistant layer is a layer which is not made of the same material as the other metal layers, for example a certain type of steel. Rather, it consists of an inorganic material, normally non-metallic, for example a carbide, an oxide or a nitride. To achieve high hardness and wear resistance, a coating of molybdenum is also contemplated.
These additional layers however cannot be applied as the other metal layers by heat bonding or forging, b
Gahlert Stefan
Wurst Bert G.
C & E. Fein GmbH & Co.
St. Onge Steward Johnston & Reens LLC
Watts Douglas D.
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